1. Field of the Invention
The present invention relates to code division multiplex radio equipment with an interference canceler.
2. Description of the Related Art
As a next-generation digital mobile communications method, a radio access method using a code division multiple access (CDMA) method is being examined and put into practical use. The CDMA method is a multiple access method using a spectrum diffusion communications method. In the CDMA method, a plurality of channels or user""s transmission data are multiplexed by a code and are transmitted through a transmission line, such as a radio circuit and the like. The CDMA method is an interference restriction type system where system capacity is restricted by interference due to the incomplete orthogonality of a code between users, and an interference elimination technology is useful for the increase of system capacity.
FIG. 1 shows the basic configuration of a multi-stage type parallel interference canceler.
The interference canceler shown in FIG. 1 is particularly applied to a base station in a CDMA communications system. Receiving signals are transmitted to interference replica generation units 1a-1 to 1a-n provided for each user. The interference replica generation units 1a-1 to 1a-n generate both the interference replica signal and symbol replica signal of the signal received from each user. The receiving signal is inputted to a delayer 2a, is delayed by a time required for the interference replica generation units 1a-1 to 1a-n to generate both the interference replica signal and symbol replica signal, and is inputted to an interference elimination unit 3a. The interference elimination unit 3a eliminates interference components by subtracting the interference replica signals transmitted from each interference replica generation units 1a-1 to 1a-n from the receiving signal that passes through the delayer 2a in the interference elimination unit 3a. Since the interference replica generation units 1a-1 to 1a-n are provided in relation to each of all users that are accommodated in a base station, the interference elimination unit 3a obtains a signal by eliminating all signals transmitted by each user from the receiving signal as interference components.
This process is performed in several stages (two stages in FIG. 1). Specifically, the signal obtained by the interference elimination unit 3a are further inputted to each of the interference replica generation units 1b-1 to 1b-n, and an interference signal component corresponding to each user is extracted from the signal outputted from the interference elimination unit 3a. The signal outputted from the interference elimination unit 3a is inputted to a delayer 2b, is delayed by a time required for the interference replica generation units 1b-1 to 1b-n to generate both the interference replica signal and symbol replica signal and is inputted to an interference elimination unit 3b. The interference elimination unit 3b eliminates the interference replica signals outputted from the interference replica generation units 1b-1 to 1b-n from the signal from the delayer 2b. The interference replica generation units 1a-1 to 1a-n generate a symbol replica signal and input it to corresponding interference replica generation units 1b-1 to 1b-n in a subsequent stage. A symbol replica signal from a previous stage is inputted to the interference replica generation units 1b-1 to 1b-n, and a new symbol replica signal is generated by combining the symbol replica signal from a previous stage with the signal from each user that is extracted from the signal from the interference elimination unit 3a. Thus the generated symbol replica signal is inputted to receivers 4-1 to 4-n provided for each user. Furthermore, the signal from the interference elimination unit 3b is also inputted to each of the receivers 4-1 to 4-n, and each of the receivers 4-1 to 4-n demodulates and receives the signal transmitted from each user.
The configuration of the interference canceler shown in FIG. 1 is for a base station and a receiver receives both the interference replica signal obtained by eliminating all receiving signals from each user as interference components and the symbol replica signal obtained by demodulating a signal from each user. Theoretically, it is all right if signals other than a signal from a target user are eliminated and the user signal is demodulated from the remaining signal after interference elimination. However, since in a base station, signals from all users must be received, the configuration becomes very lengthy if a circuit is configured based on the principle described above. Therefore, the system is configured so that both an interference replica signal obtained by eliminating all signals from all users from a receiving signal and a symbol replica signal, which is the demodulation signal of a receiving signal from each user can be received. It is also all right if only the symbol replica signal, which is the demodulation signal of a receiving signal from each user, is received. However, in that case, when an interference replica signal is generated, in reality the interference replica signal gains slight power due to fading and the like, and becomes a definite signal, although the power of the interference replica signal is ideally xe2x80x9c0xe2x80x9d. The circuit shown in FIG. 1 is configured utilizing the fact that a receiving characteristic is improved if this interference replica signal is used to demodulate a user signal along with a symbol replica signal.
FIG. 2 shows the configuration of the interference replica generation unit shown in FIG. 1.
The interference replica generation unit is provided with a plurality of fingers to perform RAKE-combination. Each finger includes an inverse diffusion unit 5 and a channel estimation unit 6. A receiving signal is inputted to a searcher 12. The searcher 12 extracts a timing signal for multiplying the receiving signal by an inverse diffusion code, and, the inverse diffusion unit 5 demodulates the receiving signal based on this timing. After the channel estimation unit 6 estimates the channel of the demodulated signal, a combination unit 7 combines the demodulated signal for each finger at a maximum ratio and inputs the signal to a judgment unit 8. After being temporarily judged in the judgment unit 8, the receiving signal is branched into the same number of signals as the number of the fingers. The branched receiving signals after the temporary judgment are inputted to the same number of delay restoration units 9 as the number of the fingers. The timing signal detected by the searcher 12 is inputted to the delay restoration units 9, and each of the delay restoration units 9 provides a delay to the branched signal. Thus, a signal delay corresponding to each multi-path possessed when the receiving signal is inputted to the finger, is restored. A re-diffusion unit 10 restores the signal after the temporary judgment, to which a delay is given, to a diffusion/modulation signal. A combination unit 11 combines the re-diffusion signals from each finger into an interference replica signal. The output signal of each delay restoration unit 9 is transmitted to an interference replica generation unit in a subsequent stage or a receiver as a symbol replica signal.
FIG. 3 shows the configuration in the case where an interference canceler is not introduced in radio base-station equipment.
The flow of a receiving signal is as follows. First, when an antenna 20 receives a signal, the frequency converter 22 of a transmitting/receiving panel 21 converts the receiving signal from an RF frequency to a baseband frequency. Then, A/D converters 24-1 and 24-2 convert the receiving signal from an analog signal to a digital signal. Quadrature demodulators 26-1 and 26-2 quadrature-demodulate this digital signal, and generate both an I signal and a Q signal. Filters 28-1 and 28-2 restrict the bands of the quadrature-demodulated I and Q signals. Although in this case, the A/D converter 24, quadrature-demodulator 26, and filter 28 are duplicated, this is because diversity reception using two antennae 20 is assumed. The band-restricted signal after the quadrature demodulation consists of I and Q signals for two branches. After a multiplexer 30 multiplexes the I and Q signals, the signal is transmitted to a baseband signal processing panel 50 through both a backboard interface 32 and a backboard 52. The baseband signal processing panel 50 receives the signal transmitted from the transmitting/receiving panel 21 through a baseband signal interface 52 and a demultiplexer 54 demultiplexes the receiving signal into I and Q signals for two branches corresponding to two antennae 20. Although a transmitting/receiving unit and a baseband signal-processing unit are called a transmitting/receiving panel 21 and a baseband signal-processing panel 50, respectively, this is because the transmitting/receiving unit and the baseband signal processing unit are both composed of one or more boards. The receiving signal that has been demultiplexed into the I and Q signals of each branch by the demultiplexer 54, is inputted to a searcher 60 for each branch, and the searcher 60 extracts a path delay timing signal. An inverse diffusion unit 56 uses this timing signal for inverse diffusion. After the inverse diffusion unit 56 inversely diffuses the receiving signal, a synchronous detector 58 synchronously detects the receiving signal, and a RAKE combination unit 62 performs RAKE COMBINATION FOR THE RECEIVING SIGNAL. After an error correction unit 64 corrects the error of the RAKE-combined signal, the RAKE-combined signal is outputted as receiving data.
The flow of a transmitting signal is as follows. An encoding unit 66 performs error correction encoding for inputted data, a radio-framing unit 68 generates a radio frame and both a pilot signal and a power control bit are added to the frame. Then, a diffusion unit 70 diffuses/modulates the inputted data, and a channel multiplex unit 72 multiplexes a plurality of channels that are outputted from a plurality of the diffusion units 70 provided in the baseband signal processing panel 50. In this preferred embodiment, since a W-CDMA system is assumed and one user uses a plurality of channels, a modulation unit for one user (comprising an encoding unit 66, a radio framing unit 68 and a diffusion unit 70) outputs diffusion/modulation signals for a plurality of channels. Then, a MUX 74 multiplexes diffusion/modulation signals for all users provided in the baseband signal processing panel 50, and a transmitting signal is outputted to a backbone wiring through a down backboard interface 76. A transmitting panel 21 receives the transmitted signal through a down backboard signal interface 34. Although one transmitting panel 21 is provided for one transmitting/receiving frequency, a plurality of baseband signal processing panels 50 are provided depending on the number of accommodated users. Therefore, if a plurality of user transmitting signals from a plurality of baseband signal processing panels 50 use one frequency, for example, a plurality of transmitting signals are transmitted to one transmitting/receiving panel 21 from a plurality of baseband signal processing panels 50. Therefore, the transmitting/receiving panel 21 inputs signals received from a plurality of baseband processing panels 50 to a multiplex processing unit 36 using a down backboard signal interface 34, multiplexes the transmitting signals from the plurality of baseband signal processing panels 50 into a plurality of pairs of I and Q signals. After a filter 38 restricts the bands of the I and Q signals multiplexed in this way, a quadrature modulator 40 quadrature-modulates the I and Q signals. Then, an D/A converter 42 converts the I and Q signals into analog signals, a frequency converter 22 converts the analog signals into RF-band signals, and an antenna 20 transmits the RF-band signals.
FIG. 4 shows the conventional configuration in the case where radio base-station equipment is provided with an interference canceler.
In FIG. 4, the same constituent components as described in FIGS. 1 through 3 are denoted by the same reference numbers.
The flow of a receiving signal is as follows. First, when an antenna 20 receives a signal, the frequency converter 22 of a transmitting/receiving panel 21 converts the receiving signal from an RF frequency to a baseband frequency. Then, A/D converters 24-1 and 24-2 convert the receiving signal from an analog signal into a digital signal. Quadrature demodulators 26-1 and 26-2 quadrature-demodulate this digital signal and generate both an I signal and a Q signal. Then, filters 28-1 and 28-2 restrict the bands of the quadrature-demodulated I and Q signals. Although in this case, the A/D converter 24, quadrature-demodulator 26, and filter 28 are duplicated, this is because diversity reception using two antennae 20 is assumed. After a multiplexer 30 multiplexes the I and Q signals, the signals are transmitted to an interference elimination circuit 78 through both a backboard interface 32 and a backboard wiring. The interference elimination circuit 78 receives the signal transmitted from the transmitting/receiving panel 21 through a backboard signal interface 80, and a demultiplexer 82 demultiplexes the receiving signal into I and Q signals for each branch. The I and Q signals demultiplexed in this way are inputted to an interference replica/symbol replica generation units 83-1 and 83-2 provided for each branch and then are inputted to a searcher 12. The searcher 60 extracts the timing signal of a delay wave due to multi-paths against one channel. This timing signal is transmitted to the inverse diffusion unit 5 of each finger, and the inverse diffusion unit 5 inversely diffuses and demodulates the receiving signal of one channel. After a channel estimation unit 6 estimates the channel of the inversely-diffused/demodulated receiving signal, a combination unit 7 combines the signals of each finger at a maximum ratio and the signals are inputted to a judgment unit 8. After the judgment unit 8 temporarily judges the receiving signal, the receiving signal is branched again into the same number of signals as that of fingers and a delay restoration unit 9 restores the delay possessed before the combination unit 7 performs RAKE-combination for the receiving signal, based on the timing signal extracted by the searcher 12. Then, a re-diffusion unit 10 restores the receiving signal to the diffusion/modulation signal. A combination unit 11 combines the re-diffusion signals from each finger. Furthermore, an addition unit 84 sums a plurality of channels of the signals combined for each channel by the combination unit 11, and inputs the summed signal to an interference elimination unit 3 as an interference replica signal.
The output signal of the delay restoration unit 9 is transmitted to a baseband signal processing panel 50 through the interference replica generation unit in a subsequent stage, which is not shown in FIG. 4 or a backboard interface 86. The interference elimination unit 3 divides the receiving signal delayed by a delayer 2 by a process time required to generate an interference replica signal, by the combined interference replica signal. Thus, interference components can be eliminated from the receiving signal. The interference-eliminated receiving signal is transmitted to the baseband signal processing panel 50 through a backboard interface 86. In the baseband signal processing panel 50, a backboard interface 52 receives both the interference-eliminated signal transmitted from an interference elimination circuit 78 and a symbol replica signal, and a DMUX 54 demultiplexes the signals into the I and Q signals for each branch. After inversely diffusing the interference-eliminated receiving signal in the timing obtained by a searcher 60, an inverse diffusion unit 56 combines the receiving signal with a symbol replica signal transmitted from the interference elimination circuit 78, and a synchronous detection unit 58 synchronously detects the combined signal. Then, a RAKE-combination unit 62 performs RAKE-combination for the signal. After correcting the error of the RAKE-combined signal, an error correction unit 64 outputs the signals as receiving data.
Since the flow of a down signal is the same as that in the conventional configuration where an interference canceler is not introduced, the description is omitted.
As described above, if an interference canceler is introduced into base-station equipment into which an interference canceler is not introduced due to the conventional technology, the interference canceler is to be introduced between a transmitting/receiving panel and a baseband signal processing panel, and thereby there is no need for a backboard for connecting a transmitting/receiving panel with a baseband signal processing panel. However, if an interference canceler panel is installed in advance and an interference canceler is not provided, signals simply pass through this interference canceler panel and thereby the mounting density of an entire apparatus is reduced, which is a problem.
It is an object of the present invention to provide radio equipment for solving the problem of the prior art described above, requiring no modification of a backboard or minimizing the extension of a signal wire when an interference canceler is introduced and introducing the interference canceler without the great reduction of the channel mounting density of radio base-station equipment.
The radio equipment in the first aspect of the present invention adopts a code division multiple access method. The radio equipment comprises a transmitting/receiving panel for receiving signals from an antenna, outputting the receiving signals after performing a prescribed process for the receiving signal and simultaneously delaying the receiving signal by a prescribed time, a removable baseband signal processing panel for demodulating data by inversely diffusing/demodulating the receiving signal transmitted from the transmitting/receiving panel and a removable interference canceler panel for generating an interference replica signal to be used to eliminate interference components included in the receiving signal, based on the signal received from the transmitting/receiving panel and returning the interference replica signal to the transmitting/receiving panel. The transmitting/receiving panel eliminates interference components by subtracting the interference replica signal transmitted from the interference canceler panel from the delayed receiving signal, inputs the receiving signal after the interference elimination to the baseband signal processing panel and enables the baseband signal processing panel to demodulate data based on the receiving signal after the interference elimination.
The radio equipment in the second aspect of the present invention adopts a code division multiple access method. The radio equipment comprises transmitting/receiving unit for receiving signals from an antenna, outputting the receiving signals after performing a prescribed process for the receiving signal and simultaneously delaying the receiving signal by a prescribed time, removable baseband signal processing unit for demodulating data by inversely diffusing/demodulating the receiving signal transmitted from the transmitting/receiving unit and removable interference canceler unit for generating an interference replica signal to be used to eliminate interference components included in the receiving signal based on the signal received from the transmitting/receiving unit and returning the interference replica signal to the transmitting/receiving unit. The transmitting/receiving unit eliminates interference components by subtracting the interference replica signal transmitted from the interference canceler unit from the delayed receiving signal, inputs the receiving signal after the interference elimination to the baseband signal processing unit and enables the baseband signal processing unit to demodulate data based on the receiving signal after the interference elimination.
The signal processing method of the radio equipment of the present invention adopts a code division multiple access. The signal processing method comprises (a) receiving a signal from an antenna, outputting the receiving signal after performing a prescribed process for the receiving signal and simultaneously delaying the receiving signal by a prescribed time in a transmitting/receiving panel, (b) demodulating data by inversely diffusing/demodulating the receiving signal transmitted from the transmitting/receiving panel in a removable baseband signal processing panel and (c) generating an interference replica signal to be used to eliminate interference components included in the receiving signal based on the signal received from the transmitting/receiving panel and returning the interference replica signal to the transmitting/receiving panel. In the transmitting/receiving panel, by subtracting the interference replica signal transmitted from the interference canceler unit from the delayed receiving signal in step (c), interference components are eliminated and data are demodulated based on the receiving signal after the interference elimination in step (b).
According to the present invention, since a transmitting/receiving panel eliminates interference components using an interference replica signal, the number of wires in an interface between a transmitting/receiving panel and an interference canceler panel, and the number of wires of an interference between a transmitting/receiving panel and a baseband signal processing panel can be made the same or almost the same. Therefore, by installing a board with an interference canceler in a prescribe position as occasion arises, an interference elimination function (interference canceler) can be easily introduced without the increase or modification of wiring.
In the equipment in the second aspect of the present invention, transmitting/receiving unit, baseband signal processing unit and interference canceler unit can also be composed of a plurality of boards, and the number of boards of each of them is not limited to one.